The effect of sprays on the fauna of apple trees. I. The influence of winter wash, captan, and lime-sulphur on the interaction of populations of Panonychus ulmi (Koch) (Acariña: Tetranychidae) and its predator, Blepharidopterus angulatus (Fall.) (Heteroptera: Miridae).
Part 1: The influence of routine sprays of winter wash (0.1 % DNOC+3.0% petroleum oil), lime-sulphur and captan on populations of P. ulmi and its predators was studied from 1953 to 1959 in a 5-acre apple orchard. During this period there were 2 marked fluctuations in the populations of both P. ulmi and B. angulatus, the only predator present in numbers. Highest populations of the mite occurred in 1956 and 1958, whereas those of B. angulatus occurred in 1957 and 1959, coinciding in both years with a drastic reduction in the numbers of mites. Although DNOC-petroleum oil and lime-sulphur had some acaricidal effect on mite populations, the full extent of the population changes was largely determined by treatment effects on the predator. Populations of P. ulmi were inversely proportional to those of B. angulatus, which were generally highest on plots treated with captan, and lowest where winter wash+lime-sulphur was used. The numbers of mites and eggs per leaf recorded at the peak of the second cycle for the treatments with the least and greatest effects on B. angulatus were: 20 (captan), 85 (lime-sulphur), 220 (winter wash+captan) and 220 (winter wash + lime-sulphur). B. angulatus was observed also to feed on leaf hoppers and, when the predator was abundant in 1959, there were fewer leaf hoppers. Typhlodromus mites were observed only on the captan-treated plots; their numbers were smaller in years when B. angulatus was abundant. [From author's summary].